1. Field of the Invention
The present invention relates to a melanogenesis-inhibiting preparation for external application, which contains 5-hydroxy-2-methoxymethyl-.gamma.-pyrone as an active ingredient and which is effective for the remedy of and prevention of chromatosis such as chloasma (liver spots) and for whitening the human skin.
2. Prior Art
For a long time, a cosmetic material containing a peroxide such as hydrogen peroxide or zinc peroxide has been used, for the purpose of removing blotches such as spots or freckles which appear on the skin.
However, the peroxides are extremely unstable and, therefore, problems arise as to their storage stability. Additionally, stable incorporation of such a peroxide into a cosmetic ,base is difficult and the peroxides themselves do not have a sufficient whitening effect.
On the other hand, a cosmetic material containing vitamin C, cystein or colloidal sulfur has become utilized for the purpose of skin-whitening. However, the effect of such substances is still unsatisfactory.
Recently, kojic acid has been found to be effective as a substance for inhibiting formation of melanine in the human skin. Accordingly, a kojic acid-containing skin-whitening cosmetic material (Japanese Patent Publication No. 56-18569), a skin-whitening cosmetic material containing an ester of kojic acid with an aromatic carboxylic acid such as cinnamic acid or benzoic acid (Japanese Patent Publication No. 60-10005), and a skin-whitening cosmetic material containing an aliphatic carboxylic acid diester of kojic acid or an aliphatic carboxylic acid monoester of kojic acid (Japanese Patent Publication Nos. 61-60801 and 60-7961) have been proposed.
As mentioned above, kojic acid and kojic acid esters are known as excellent substances capable of inhibiting melanogenesis (formation of melanine). When a preparation of a cosmetic material or a medicine for external application formed to contain these substances as active ingredients is applied to the skin, an excellent whitening and melanogenisis-inhibiting effect are exhibited without injuries to the skin. Thus, kojic acid and kojic acid esters are known to be usable as an active ingredient for a cosmetic material or a medicine for external application.
However, other substances capable of inhibiting melanogenesis more effectively are strongly desired.
The object of the present invention is to provide a melanogenesis-inhibiting preparation for external application, which contains a substance having a higher melanogenesis-inhibiting activity than the above-mentioned kojic acid or derivatives thereof such as kojic acid esters.
In order to attain the above-mentioned object, the present inventors widely investigated and repeatedly studied various substances having a higher melanogenesis-inhibiting activity among kojic acid derivatives and, as a result, have found that 5-hydroxy-2-methoxymethyl-.gamma.-pyrone which is a methyl ether of kojic acid has an extremely high tyrosinase activity-inhibiting effect and therefore has an effect of whitening B16 cells. On the basis of such findings, the present invention has been accomplished.